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ground vs air source heat pumps
 Started by  thecanuck
 22 Jun 2010, 10:06 AM


My new neighbour who is converting an old barn across the road from me has recently been admiring my air source heat pump installation. He definitely wants to install a heat pump but, as he has 2 acres of garden, he is hooked on the idea of going with ground source.
 
As much as I believe in heat pumps, I'm not sure that's such a good idea. Why should he spend 4k-6k more on a heat pump installation just because he has a big garden? From what I've read recently, one of the major advantages that gshp have had over ashp (I'm talking air to water here) is their ability to keep pumping out heat even during the defrost cycle. I'm sure I read recently that new ashp models have overcome this, haven't they?
 
Ok, I can see that using the ground as a heat source in Winter would deliver a higher coefficient of performance than using the air. However, this must be at least partly made up as soon as the air temperature gets warmer in late Spring through to early Autumn.
 
Does anyone know of any quantitative analysis in existence that would shed light on this dilemna? Everyone seems to have 'a view' but there seems to be little science or concrete analysis to back any of these views up (discounting any marketing blurb from manufacturers, of course).
tony
Try reading on the greenbuilding forum there is a guy on there Paul from Montreal who knows his stuff
 
gshp is more efficient than ashp and for sure colder countries is the better choice
 
I have no formal heating system in my new house -- if I put all the lights on it gets too warm even last winter Smile
 
thecanuck
thanks, Tony. I am Canadian but I guess I should have specified that I've been living in England for nearly 20 years now! My neighbour is a Yorkshire man converting an old barn into a 3-bed home for his retirement. Did you self-build to have a house so well insulated? to what standard did you insulate?
 
So, just to clarify to everyone, my question is about GSHP vs ASHP in the UK, not in Canada.
 
tony
see <tonyshouse.info>
 
Haggis
ASHP (in the UK) is as significant detail. In the UK, in winter, this involves sucking HUMID air into an ASHP with much of its pipework containing liquids at well below zero. The problem is not only the decrease in COP, but the real danger if icing-up. Another tack you could confuse a salesman with is "Why do relatively small ASHPs need a 3, 6 or 8Kw immersion heater element" - I'll whisper the answer - "Because the industry is battling with the icing-up problem in ASHPs located in humid climates and fitting a non-green compliant heating element of absurd requirements is a crude solution. In my opinion ASHPs should not be marketed in the northern UK.
Incidentally - my GSHP worked a treat last winter, when snowed in for days - most of the year, like Tony the house insulation is so good that the pump is seldom on!
 
thecanuck
Thanks, Haggis. Does that mean that your COP stays roughly the same all year round then? Do you have a buffer tank with your GSHP?
 
technicalm
Air source is a no brainer. they have improved so much in recent years theres no use for ground source unless you;re a mad scientist.
 
The problem is, the samee old hacks rattle out the same stories of years old doom!
 
lower installation cost, brilliant efficeincy and no wondering about the pipes burried in the garden.
 
we fitted one in ripon, humid, cold north yorkshire and it's ace. and another in hull, a few yards from the humber..... and it's ace. another on the lincolnshire coast across a FIELD from the sea, been in 2 years and owners over the moon.
 
it helps to have an installer knows what they're doing and we do - and consider this - the largest growth in sales of any heating appliance - oh...."but them air source things dont work.".......... yes they do. there are loads in scandinavia.
 
And its cold.....very cold.....and wet.....very wet.......
 
happy days.
 
heinbloed
The average anual OP for air sourced HPs seems to be well below 3, more around 2.6 . In worst case scenarious only around 1 .....
 
See
 
http://wp-verbrauch.in-tostedt.de/index.php?lang=en
 
 
Enter your data ( if you run a HP) to help others to get an overview.
And get your electricity consumption GUARANTEED by the manufacturer. They have the software to calculate/give such a guarantee. Installers come and go.....
 
thecanuck
Thanks, technicalm and heinbloed. The facts seem to confirm that HPs generally are much more efficient form of heating than all other traditional except for mains gas where the difference is perhaps not so pronounced.
 
I've concluded that there is a kind of "merit order" of HPs: with open coil GSHPs using wells or water to water HPs using water from lakes or rivers being at the top of the HP efficiency table; closed system GSHPs are not far behind though and ASHPs seem to come last - if only because their source of heat is by far the most variable in temperature. If you have got access to a lake or have a decent size garden, a good ASHP is still a better option than oil and lpg (and sometimes even mains gas).
 
So, in consultation with me, my neighbour has decided to go for a GSHP because he has 3-4 acres of land to use and he doesn't his heating electricity bills to be subject to the vagaries of the British Winter weather! The fact that some manufacturers are still offering a "cashback" of 1,000-1,500 this year also helped as this will cover the cost of the groundworks.
 
Technicalm, I'd be interested in getting your company details. Can you please email them to me on mich20@tiscali.co.uk?
 
And now, onto high heat output rads...
 
GBP-Keith
Beware of salesmen blowing their own trumpet!
 
technicalm
None of that, and I'm not a heat pump salesman, I work in technical.
 
The fact is, air source can be fantastic when specified right and matched to the system properly.
 
If that isnt done, you're on a hiding to nothing.
 
Sadly, heat pumps often get a bad press when there's nothing wrong with the heat pump - rather it's been specified incorrectly.
 
and that's why we dont employ salesmen....
 
Happy days.
 

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